The (very) simple answer is:
If you are using a 32 bit Operating System and you don't combine Poser with one of the other applications that P7P interfaces with, DON'T buy P7P (you will have no extra features).
If you do combine Poser with other applications but do so on a 64 bit OS, DON'T buy P7P (the interfaces only work on 32 bit versions of the programs).
If you do not have the possibility to use the special upgrade prices, DON'T buy P7P (it's just too expensive).

If you are using just Poser on a 64 bit OS and you can use the special price, you may consider it as it does offer some features that might be useful. The 64 bit rendering capabilities (only when you are using a 64 bit OS), the Queue Manager (only on powerful machines) are improvements for people using just Poser for for large and complex renders.

If you are combining Poser with other programs, you may consider buying P7P but the interface has it's problems and most people have used other means of interfacing with better results.

So to answer your question: NO, unless you are using a 64 bit OS, are using just Poser, are rendering large and complex scenes, can afford to price, and want to be on the latest version.